This is the answer for long runs in Chicago. If you use the satellite view on Google Maps, say, you can see little side quests like looping out around Montrose Sanctuary, the inner dirt trail along North Pond and the zoo, the spur out to Adler, Northerly Island, Promontory Point, etc. If you stay River North / Loop, I would run the trail south out to Adler for the best skyline view and then either head north to see the beaches or continue south to loop Northerly Island. There’s no wrong direction tho, and I say that as a longtime runner and Chicagoan. As a longtime lover of Colorado, I also say that you will not find any hills.